Measurement apparatus and measurement method

ABSTRACT

A measurement apparatus and a measurement method capable of speedily and accurately measuring an edge shape are provided. A measurement apparatus according to an aspect of the present disclosure includes an objective lens positioned so that its focal plane cuts across an edge part of a substrate, a detector including a plurality of pixels and configured to detect a reflected light from the edge part of the substrate through a confocal optical system, an optical head in which the objective lens and the detector are disposed, a moving mechanism configured to change a relative position of the optical head with respect to the substrate so that an inclination of the focal plane with respect to the substrate is changed, and a processing unit configured to measure a shape of the edge part.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Application No.2018-146053, entitled “MEASUREMENT APPARATUS AND MEASUREMENT METHOD”,and filed on Aug. 2, 2018. The entire contents of the above-listedapplication are hereby incorporated by reference in their entirety forall purposes.

BACKGROUND

The present disclosure relates to a measurement apparatus and ameasurement method for measuring an edge shape.

Japanese Unexamined Patent Application Publication No. 2007-206441discloses a confocal image pickup apparatus for observing a peripheraledge of a semiconductor wafer over the entire circumference thereof. Theconfocal image pickup apparatus disclosed in Japanese Unexamined PatentApplication Publication No. 2007-206441 includes an image pickup opticalsystem and a rotatable table that supports a semiconductor wafer. Theimage pickup optical system includes an apparatus that generates alinear light beam and a linear sensor.

Japanese Unexamined Patent Application Publication No. 2007-163265discloses a measurement apparatus for measuring a cross-sectional shapeof a peripheral edge of a semiconductor wafer. The measurement apparatusdisclosed in Japanese Unexamined Patent Application Publication No.2007-163265 includes two confocal image pickup devices. Each of theimage pickup devices includes means for generating a linear light beam,an objective lens that concentrates the light beam, and a linear imagesensor. One of the image pickup devices takes an image of one of theinclined surfaces of the peripheral edge while the other image pickupdevice picks up an image of the other inclined surface. The measurementapparatus measures the cross-sectional shape based on a Z-position ofthe objective lens at which a brightness value is maximized by scanning(i.e., continuously or successively moving) the objective lens in anoptical-axis direction (i.e., a Z-direction).

SUMMARY

In order to improve a yield rate of chips near an edge of asemiconductor wafer, quality control near the edge is important. Aprofile of an edge of a semiconductor wafer depends on the orientationof crystallization and changes according to the angle thereof.Therefore, an edge shape may change according to the orientation ofcrystallization and may change asymmetrically in the vertical direction.Therefore, it is desired to accurately measure an edge shape.

The present disclosure has been made in view of the above-describedcircumstances and provides a measurement apparatus and a measurementmethod capable of speedily and accurately measuring an edge shape.

A first exemplary aspect is a measurement apparatus including: anobjective lens positioned so that its focal plane cuts across an edgepart of a substrate, and configured to concentrate illumination light sothat a linear illumination area is formed on the focal plane; a detectorincluding a plurality of pixels arranged along a direction of the linearillumination area, and configured to detect a reflected light from theedge part of the substrate through a confocal optical system; an opticalhead in which the objective lens and the detector are disposed; a movingmechanism configured to change a relative position of the optical headwith respect to the substrate so that an inclination of the focal planewith respect to the substrate is changed; and a processing unitconfigured to measure a shape of the edge part based on a position ofthe detector at which intensity of the reflected light reaches a peak.

The above-described measurement apparatus may further include arotatable stage configured to rotate the substrate, in which thereflected light may detected while rotating the rotatable stage.

In the above-described measurement apparatus, the moving mechanism mayrotationally move the optical head around a rotational axis; and therotational axis may be perpendicular to a plane including a Z-axisparallel to a thickness direction of the substrate and an optical axisof the objective lens, and pass through the inside of the substrate.

In the above-described measurement apparatus, the processing unit mayconvert the position at which the intensity of the reflected lightreaches the peak in the detector into an edge position on a planeincluding a Z-axis along a thickness direction of the substrate and anoptical axis of the objective lens.

In the above-described measurement apparatus, the processing unit mayobtain two edge positions disposed on both sides of the optical axis ofthe objective lens.

In the above-described measurement apparatus, a graph showing angledependence of a feature value representing an edge shape may bedisplayed.

Another exemplary aspect is a measurement method using a measurementapparatus, the measurement apparatus comprising: an objective lenspositioned so that its focal plane cuts across an edge part of asubstrate, and configured to concentrate illumination light so that alinear illumination area is formed on the focal plane; a detectorcomprising a plurality of pixels arranged along a direction of thelinear illumination area, and configured to detect a reflected lightfrom the edge part of the substrate through a confocal optical system;and an optical head in which the objective lens and the detector aredisposed, the measurement method comprising: changing a relativeposition of the optical head with respect to the substrate so that aninclination of the focal plane with respect to the substrate is changed;and measuring a shape of the edge part based on a position of thedetector at which intensity of the reflected light reaches a peak.

In the above-described measurement method, the reflected light may bedetected while rotating the substrate.

In the above-described measurement method, in the changing the relativeposition of the optical head, the optical head may be rotationally movedaround a rotational axis; and the rotational axis may be perpendicularto a plane including a Z-axis parallel to a thickness direction of thesubstrate and an optical axis of the objective lens, and pass throughthe inside of the substrate.

In the above-described measurement method, in the measuring the shape ofthe edge part, the position at which the intensity of the reflectedlight reaches the peak in the detector may be converted into an edgeposition on a plane including a Z-axis along a thickness direction ofthe substrate and an optical axis of the objective lens.

In the above-described measurement method, in the measuring the shape ofthe edge part, two edge positions disposed on both sides of an opticalaxis of the objective lens may be obtained.

In the above-described measurement method, a graph showing angledependence of a feature value representing an edge shape may bedisplayed.

According to the present disclosure, it is possible to provide ameasurement apparatus and a measurement method capable of speedily andaccurately measuring an edge shape.

The above and other objects, features and advantages of the presentdisclosure will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an overall configuration of ameasurement apparatus according to an embodiment;

FIG. 2 shows an optical system provided in an optical head;

FIG. 3 is a flowchart showing a method for measuring an edge shape at acertain θ-angle;

FIG. 4 is a diagram for explaining a method for measuring a profile ofan edge;

FIG. 5 shows positions of focal planes when an A-axis angle is changed;

FIG. 6 shows confocal images and Y-direction profiles according to theA-axis angle;

FIG. 7 is a graph showing a peak position for each A-axis angle;

FIG. 8 shows peak positions when the A-axis angle is +30°;

FIG. 9 shows edge positions on an RZ-plane;

FIG. 10 shows a measured edge profile;

FIG. 11 is a flowchart showing a method for measuring an edge shape overthe entire circumference;

FIG. 12 is a diagram for explaining feature values of an edge part;

FIG. 13 is a graph showing changes in a wafer thickness WT according toa θ-angle;

FIG. 14 is a graph showing changes in a TB angle TBA according to theθ-angle;

FIG. 15 is a graph showing changes in an APEX length AP according to theθ-angle;

FIG. 16 is a graph showing changes in a TB height TBL1 according to theθ-angle;

FIG. 17 shows an average profile of an edge; and

FIG. 18 shows unevenness data of an edge.

DETAILED DESCRIPTION

Examples of embodiments according to the present disclosure will bedescribed hereinafter with reference to the drawings. The followingexplanation is given for showing preferable embodiments according to thepresent disclosure and the technical scope of the present disclosure isnot limited to the below-shown embodiments. The same symbols areassigned to the same or corresponding components throughout the drawingsand duplicated explanations are omitted as appropriate for clarifyingthe explanation.

First Embodiment

An embodiment according to the present disclosure is explainedhereinafter with reference to the drawing. A configuration of ameasurement apparatus according to this embodiment is explained withreference to FIG. 1. FIG. 1 schematically shows an overall configurationof a measurement apparatus. A measurement apparatus 100 measures a shapeof an edge part 31 of a substrate 30. The measurement apparatus 100includes an optical head 10, a stage 20, a moving mechanism 40, and aprocessing unit 50. Note that in the following explanation, a verticallyupward direction is referred to as a Z-axis positive direction. Further,it is assumed that the Z-direction is parallel to a thickness directionof the substrate 30. Further, a radial direction of the circularsubstrate 30 is referred to as an R-direction.

The substrate 30, which is an object to be measured, is placed on thestage 20. The substrate 30 is, for example, a circular substrate such asa semiconductor wafer. Note that the substrate 30 may have a notch(es)and an orientation flat(s). The stage 20 may hold the substrate 30 bymeans of a vacuum chuck or the like. The edge part 31 of the substrate30 projects from the stage 20. That is, the stage 20 has a disk-likeshape having a diameter smaller than that of the substrate 30. Note thata surface on the Z-axis positive side of the substrate 30 is referred toas a front surface 33 and a surface on the Z-axis negative side of thesubstrate 30 is referred to as a rear surface 34. The front and rearsurfaces 33 and 34 of the substrate 30 are surfaces perpendicular to theZ-direction. The front surface 33 of the substrate 30 is apattern-formed surface on which a pattern is formed.

The stage 20 is a rotatable stage and is configured to rotate thesubstrate 30 around the Z-axis. That is, the substrate 30 is rotated ina θ-direction. The Z-axis, which coincides with the rotational axis ofthe stage 20, passes through the center of the substrate 30 and isparallel to the vertical direction. The rotational angle of the stage 20around the Z-axis is referred to as a θ-angle. The stage 20 can rotatethe substrate 30, for example, at a constant rotational speed.

An optical system for measuring an edge shape is provided in the opticalhead 10. Specifically, the optical head 10 includes a line confocaloptical system. The line confocal optical system includes a lightsource, a lens, a mirror, a sensor, and so on. The optical systemprovided in the optical head 10 will be described later. The opticalaxis of the optical head 10 is referred to as an optical axis OX.

The optical head 10 is attached to the moving mechanism 40. That is, themoving mechanism 40 supports the optical head 10 so that the opticalhead 10 can be moved. The moving mechanism 40 moves the optical head 10along a circular arc (indicated as optical heads 10 a to 10 d in FIG.1). Note that the center of the circular arc is referred to as a centerO. The moving mechanism 40 includes a driving mechanism 41 and a guide42. The guide 42 has a semi-circular arc shape. The center O of thecircular arc of the guide 42 is positioned at the edge part 31 of thesubstrate 30. Therefore, one of the ends of the guide 42 is disposedabove the substrate 30 (on the Z-axis positive side) and the other endis disposed below the substrate 30 (on the Z-axis negative side).

The driving mechanism 41 includes an actuator like a servo motor fordriving the optical head 10. The optical head 10 is driven by thedriving mechanism 41 and thereby is moved along the guide 42. That is,the optical head 10 rotationally moves. In this way, the inclination ofthe optical axis OX of the optical head 10 is changed. The rotationalaxis of the rotational movement of the optical head 10 is referred to asan A-axis. The A-axis passes through the center O located inside thesubstrate 30 and is parallel to the direction perpendicular to thedrawing surface (i.e., the surface of the paper). That is, the A-axis isperpendicular to the plane that includes the Z-axis and the optical axisOX, and passes through the inside of the substrate 30.

An angle around the A-axis (hereinafter referred to as an A-axis angle)is defined as shown in FIG. 1. It is assumed that the A-axis angle is+90° when the optical head 10 is directly above the center O (i.e.,located at the position indicated by the optical head 10 a). It is alsoassumed that the A-axis angle is −90° when the optical head 10 isdirectly below the center O (i.e., located at the position indicated bythe optical head 10 d). When the A-axis angle is +90° or −90°, theoptical axis OX of the optical head 10 is parallel to the Z-axisdirection. When the A-axis angle is 0°, the optical head 10 is locateddirectly beside the substrate 30 and the optical axis OX of the opticalhead 10 is perpendicular to the Z-axis. When the A-axis angle is 0°, theoptical axis OX is parallel to the horizontal direction and passesthrough the center of the substrate 30.

For example, it is possible to measure a cross-sectional profile of theedge part 31 of the substrate 30 by scanning (i.e., continuously orsuccessively moving) the optical head 10 around the A-axis withoutrotating the stage 20. Specifically, it is possible to measure an edgeprofile of the substrate 30 on a plane that intersects the center O andis parallel to the drawing surface. The plane on which the edge profileis measured is referred to as an RZ-plane. The rotational movement ofthe optical head 10 around the A-axis is a movement on the RZ-plane.

The processing unit 50 is, for example, a computer that includes aprocessor, a memory, and so on, and performs a process for measuring theedge shape. Further, the processing unit 50 includes a monitor fordisplaying a measurement result and an input device such as a keyboard,a mouse, a touch panel, and the like.

The processing unit 50 controls the driving mechanism 41 and the stage20. The processing unit 50 collects data on the A-axis angle of thedriving mechanism 41 and the θ-angle. The processing unit 50 collectsdetection data obtained by the optical head 10. Then, the processingunit 50 associates the detection data with the angle data and storesthem in the memory or the like. The processing unit 50 performs aprocess for measuring an edge shape of the substrate 30 based on thedetection data and the angle data. The process performed by theprocessing unit 50 will be described later.

Next, a configuration of the optical head 10 is described with referenceto FIG. 2. FIG. 2 shows a configuration of an optical system provided inthe optical head 10. As described above, the optical head 10 is equippedwith the line confocal optical system 110. The line confocal opticalsystem 110 includes an illumination light source 11, a half mirror 12, alens 13, a mirror 14, a lens 15, a lens 16, an objective lens 17, and adetector 18. These optical devices are fixed to a housing or the like(not shown) in the optical head 10. Further, the moving mechanism 40rotationally moves the whole line confocal optical system 110.

Firstly, the illumination light optical system for illuminating thesubstrate 30 is described. The illumination light source 11 generateslinear illumination light. Various types of light sources such as a lamplight source, an LED (Light Emitting Diode), and a laser light sourcecan be used for the illumination light source 11. The illumination lightsource 11 is a line-light source. Alternatively, it is possible togenerate linear illumination light by using a slit or a cylindricallens.

In order to form the line confocal optical system 110, the illuminationlight forms a linear illumination area on a focal plane (or a focusplane) of the objective lens 17. Note that the focal plane is a planethat includes the focal point F and is perpendicular to the optical axisOX. On the focal plane, the long-side direction of the illumination areais defined as a Y-direction and the short-side direction thereof isdefined as an X-direction. The X- and Y-directions are perpendicular toeach other. It is assumed that the Y-direction is a direction on theRZ-plane shown in FIG. 1.

The illumination light emitted from the illumination light source 11 isincident on the half mirror 12. Half of the light incident on the halfmirror 12 passes through the half mirror 12 and the remaining halfthereof is reflected on the half mirror 12. The illumination lightreflected on the half mirror 12 becomes a parallel luminous flux by thelens 13. The illumination light, which has become the parallel luminousflux, is incident on the mirror 14. The mirror 14 reflects theillumination light toward the lens 15. The illumination light isrefracted by the lenses 15 and 16. The lenses 15 and 16 are, forexample, relay lenses. The illumination light that has passed throughthe lens 16 becomes a parallel luminous flux.

The illumination light that has passed through the lens 16 is incidenton the objective lens 17. The objective lens 17 concentrates theillumination light on the focal plane. A focal point F of the objectivelens 17 is positioned at the edge part 31 of the substrate 30. The focalpoint F is located on the optical axis OX and inside the substrate 30.Therefore, the focal point F is deviated from the surface of thesubstrate 30 and is located inside thereof. The illumination light isreflected on a surface of the substrate 30.

Next, a detection optical system for detecting a reflected lightreflected on the substrate 30 is described. The reflected lightreflected on the substrate 30 goes back the optical path of theillumination light. That is, the reflected light becomes a parallelluminous flux by the objective lens 17 and is incident on the lens 16.The lenses 16 and 15 refract the reflected light. The reflected lightthat has passed through the lens 15 is reflected by the mirror 14 and isincident on the lens 13. Then, the reflected light is refracted by thelens 13 and is incident on the half mirror 12. Half of the reflectedlight from the lens 13 passes through the half mirror 12 and enters thedetector 18.

The lens 13 is an imaging lens and concentrates the reflected light on alight receiving surface of the detector 18. The detector 18 is, forexample, a line sensor including a plurality of pixels. Specifically, aline CCD (Charged Coupled Device) or a CMOS (Complementary Metal OxideSemiconductor) line sensor can be used as the detector 18. Therefore, aplurality of pixels are arranged in a row on the light receiving surfaceof the detector 18. The plurality of pixels of the detector 18 arearranged along the Y-direction. The detector 18 detects the reflectedlight and outputs data on a detection result to the processing unit 50(see FIG. 1). That is, the detector 18 outputs, for each pixel,detection data indicating intensity of the reflected light to theprocessing unit 50.

Note that the light receiving surface of the detector 18 is positionedin a place conjugate with the focal plane of the objective lens 17. Theillumination light concentrated by the objective lens 17 forms a linearillumination area on the focal plane. On the light receiving surface ofthe detector 18, the reflected light is concentrated into a linear shapewhose longitudinal direction is parallel to the Y-direction. Thereflected light that has been reflected on a plane that is deviated fromthe focal plane in the optical-axis direction is incident on an areaoutside the pixels of the detector 18. In this way, the line confocaloptical system 110 can be formed.

In the above-described example, the detector 18, which is the linesensor, is disposed in a place conjugate with the focal plane of theobjective lens 17. However, it is also possible to form the lineconfocal optical system 110 by using a slit. For example, a slit that isformed along the linear illumination area is positioned at a placeconjugate with the focal plane. The detector 18 is disposed behind theslit so as to detect reflected light that has passed through the slit.Here, it is assumed that the detector 18 is a line sensor in which aplurality of pixels are arranged along the direction of the slit. Inthis way, the reflected light reflected on the focal plane passesthrough the slit and the reflected light reflected on the plane deviatedfrom the focal plane is shielded by the slit. In this way, the lineconfocal optical system can be formed. The detector 18 detects thereflected light through the confocal optical system and outputsdetection data to the processing unit 50.

Next, a measurement method according to this embodiment is describedwith reference to FIG. 3. FIG. 3 is a flowchart showing a method formeasuring an edge shape. Note that for simplifying the explanation, amethod for performing measurement without performing a θ-rotation by thestage 20 is described. That is, a method for measuring a profile of anedge shape at a certain θ-angle is described.

Firstly, the moving mechanism 40 scans (i.e., continuously orsuccessively moves) the A-axis (S11). That is, the moving mechanism 40rotationally moves the optical head 10. In this way, the optical head10, in which the objective lens 17, the detector 18, and the like aredisposed, is moved, so that the inclination of the optical axis OX ischanged. The moving mechanism 40 changes the relative position of theoptical head 10 with respect to the substrate 30 so that the inclinationof the focal plane with respect to the substrate 30 is changed. Forexample, the moving mechanism 40 scans the A-axis angle in a range of−90° to +90°.

The processing unit 50 stores, for each A-axis angle of the movingmechanism 40, detection data detected by the detector 18. In thisexample, it is assumed that measurement is performed by scanning theA-axis angle with a pitch of 5° (i.e., at intervals of 5°). In this way,the detector 18 detects reflected light for each A-axis angle. Needlessto say, the scanning range and the scanning pitch are not limited to anyparticular ranges and any particular pitches.

Then, the processing unit 50 acquires a profile shape at a certainθ-angle (S12). The processing unit 50 associates an A-axis angle and itsdetection data, and stores them. The processing unit 50 generates aprofile shape of an edge based on detection data for each A-axis angle.The processing unit 50 measures (i.e., determines) a shape of an edgepart based on the position of the detector 18 at which intensity ofreflected light reaches a peak.

A process for measuring a profile shape is described hereinafter withreference to FIG. 4. FIG. 4 schematically shows an edge profile P on anRZ-cross section. Note that the edge profile P is a profile line that isobtained by connecting edge positions with one another on a crosssection of the substrate 30 along the RZ-plane.

The RZ-plane is a measurement plane of the edge profile P. The focalpoint F is located on the optical axis OX of the objective lens 17 (notshown in FIG. 4) and is located inside the edge profile P of thesubstrate 30. That is, the focal point F is a point located inside thesubstrate 30. A plane that includes the focal point F and isperpendicular to the optical axis OX is a focal plane S. The center O ofthe rotational movement around the A-axis is located on the optical axisOX. Further, the optical axis OX is located on (i.e., parallel to) theRZ-plane. The center O is deviated from the focal point F. In thisexample, the focal point F is closer to the objective lens 17 than thecenter O is. Therefore, on the optical axis OX, the edge profile P(equivalent to the edge position), the focal point F (equivalent to thefocal plane S), and the center O are arranged in this order as viewedfrom the objective lens.

As described above, on the focal plane S, the objective lens 17concentrates illumination light so that the illumination light has alinear shape along the Y-direction. The Y-direction is a direction onthe RZ-plane (i.e., a direction parallel to the RZ-plane). Therefore, asshown in FIG. 4, the focal plane S obliquely cuts across an edge of thesubstrate 30. On the RZ-plane, two points at which the focal plane Scuts across the edge profile P are referred to as edge positions D andE. On the RZ-plane, the edge positions D and E are intersection pointsbetween the edge profile P and the focal plane S.

Specifically, the edge positions D and E are disposed on both sides ofthe optical axis OX. The edge position D is located on the Z-axispositive side of the focal point F and the edge position E is located onthe Z-axis negative side of the focal point F. The edge positions D andE are illuminated. In the edge profile P, a range from the edge positionD to the edge position E is referred to as a range DE. Note that therange DE is a range that does not include the edge positions D and E.The range DE is illuminated by the illumination light. However, in therange DE, the edge profile P is deviated from the focal plane S to theobjective lens side. Therefore, because of the confocal effect, theintensity of the reflected light reflected in the range DE, detected bythe detector 18 is significantly low.

A range that extends from the edge position D toward the front surface33 is deviated from the focal plane S. Similarly, a range that extendsfrom the edge position E toward the rear surface 34 is also deviatedfrom the focal plane S. Therefore, even if the range that extends fromthe edge position D toward the front surface 33 and the range thatextends from the edge position E toward the rear surface 34 areilluminated, no reflected light is detected. Therefore, in the stateshown in FIG. 4, the intensity of the reflected light reflected on theedge positions D and E is extremely high. That is, regarding theintensity of the light detected by the detector 18, the reflected lightfrom the two intersection points (i.e., the edge positions D and E)between the focal plane S and the edge profile P is dominant.

FIG. 5 is a diagram for explaining changes in the focal plane S and theedge positions D and E when the optical head 10 is rotationally movedaround the A-axis. In FIG. 5, the optical axis OX, the focal point F,the focal plane S, the edge positions D, and the edge position E shownin FIG. 4 are indicated by an optical axis OX1, a focal point F1, afocal plane S1, an edge position D1, and an edge position E1. Further,it is assumed that the optical axis OX1 is successively shifted to anoptical axis OX2 and to an optical axis OX3 through rotational movementsaround the A-axis. In this case, the focal plane S is also successivelychanged from the focal plane S1 to a focal plane S2 and to a focal planeS3. That is, through the rotational movements around the A-axis, theinclination of the optical axis OX changes, so that the inclination ofthe focal plane S also changes. The focal point F is also successivelychanged from the focal point F1 to a focal point F2 and to a focal pointF3.

The edge positions D2 and E2 are intersection points between the focalplane S2 and the edge profile P. The edge positions D3 and E3 areintersection points between the focal plane S3 and the edge profile P.The edge position D is successively shifted from the edge position D1 tothe edge position D2 and to the edge position D3 by the rotationalmovement around the A-axis. Similarly, the edge position E issuccessively shifted from the edge position E1 to the edge position E2and to the edge position E3. Therefore, it is possible to graduallychange the edge position by gradually changing the A-axis angle.

The edge profile P can be measured by obtaining the edge positions D andE for each A-axis angle. That is, the edge profile P on the RZ-plane canbe obtained by connecting the edge positions D and E which are measuredby changing the A-axis angle. In this embodiment, measurement isperformed in the state in which the focal point F is deviated from theedge position on the optical axis OX. Specifically, measurement isperformed in the state in which, even when the axis A is changed, theedge position is closer to the objective lens than the focal point F is.In other words, measurement is performed in the state in which the focalplane S always cuts across the edge irrespective of the A-axis angle.

The edge positions D and E, which are deviated from the optical axis OXand are located on the focal plane S, are illuminated by theillumination light. Then, the detector 18 detects the reflected lightfrom these edge positions D and E through the confocal optical system.

Next, a process for obtaining edge positions D and E from detection dataobtained by the detector 18 is described. FIG. 6 shows confocal imagesof the edge part 31 and detection data thereof. FIG. 6 shows confocalimages that are obtained when A=+90°, +30°, 0° and −30°, and detectiondata of reflected light. FIG. 7 shows the confocal image obtained whenA=+30° and detection data of reflected light in an enlarged manner.

Note that the confocal images shown in FIG. 6 are two-dimensional imagesobtained by scanning (i.e., successively moving) liner illuminationlight in the X-direction. Specifically, they are images obtained byscanning the illumination light by using the mirror 14 shown in FIG. 2as an optical scanner such as a galvanometer mirror. The actualmeasurement of the edge shape is carried out without taking confocalimages. In other words, scanning by the optical scanner is unnecessary.

Detection data of the reflected light is schematically shown on theright side of each confocal image. Note that data on the intensity ofthe reflected light obtained when A=+90°, +30°, 0° and −30° areindicated as detection data 61, 62, 63 and 64, respectively. Thedetection data 61 to 64 indicate profiles of the intensity of thereflected light along the Y-direction.

For example, the detection data 62 corresponding to A=+30° has twopeaks. These two peaks correspond to the edge positions D and E. Thepeak on the Y-axis positive side corresponds to the edge position D andthe peak of the Y-axis negative side corresponds to the edge position E.Because of the confocal effect, the intensity of the reflected light ishigh in pixels corresponding to the edge positions D and E and is low inpixels corresponding to the other area (e.g., the range DE in FIG. 4).That is, the pixels that correspond to the edge positions D and E becomethe peak positions of the intensity of the reflected light. Further, asthe edge positions D and E change, the peak positions also change. Thatis, the peak positions change according to the edge shape.

As shown in FIG. 7, the processing unit 50 identifies, among the pixels18 a of the detector 18, a pixel(s) in which the intensity of thereflected light is the highest as a peak pixel(s) 18 p. Then, theprocessing unit 50 determines the pixel position of the peak pixel 18Pas the peak position. The peak position is obtained in the Y-directionprofile of the intensity of the reflected light acquired for each A-axisangle. The edge position D corresponds to 307 (pixel) and the edgeposition E corresponds to 550 (pixel). For example, the center pixel ofthe detector 18 corresponds to 512 (pixel). That is, the pixel positionsare represented by integers of 0 to 1,024.

Note that as shown in FIG. 6, when the A-axis angle is +90°, only onepeak appears in the detection data 61. This is because the edge positionD goes out of the field of view of the detector 18. That is, on theRZ-plane, an angle formed by the focal plane S and the edge profile Pbecomes small near the front surface 33 or the rear surface 34. As aresult, the distance from the optical axis OX to the edge position D orE increases. When the focal plane S and the edge profile P become almostparallel to each other, the edge position D or E goes out of the fieldof view of the detector 18.

Therefore, only one peak may appear when the A-axis angle is close to+90° or −90°. In this case, the processing unit 50 may obtain only onepeak position. Alternatively, neither of the two peaks may appear whenthe A-axis angle is close to +90° or −90°. In this case, the processingunit 50 may obtain no peak position.

FIG. 8 is a graph showing peak positions for each A-axis angle. In FIG.8, a horizontal axis indicates A-axis angles (deg) and a vertical axisindicates peak positions (pixel). FIG. 8 shows a measurement result whenthe A-axis angle is changed at intervals of 5°. For each angle, peakpositions corresponding to the edge positions D and E are plotted. Dataabove the center pixel (512) corresponds to the edge position E and databelow the center pixel (512) corresponds to the edge position D.

When the A-axis angle is close to +90°, no peak corresponding to theedge position D appears. Therefore, no peak position corresponding tothe edge position E is plotted. Further, when the A-axis angle is closeto −90°, no peak corresponding to the edge positions D and E appears.Therefore, no peak position is plotted.

Peak positions can be converted into positions (coordinates) on theRZ-plane. Specifically, the processing unit 50 geometrically obtainsR-positions and Z-positions from peak positions (pixel) by using theA-axis angle and the setting of the optical system. FIG. 9 is a graph inwhich the peak positions (pixel) shown in FIG. 8 are converted intoR-positions and Z-positions.

For example, the following Expressions (1) and (2) are conversionformulas for calculating an R-position (R1) and a Z-position (Z1) frompeak positions (pixel).

R1=r0*cos(A)+(p1−pc)*k*sin(A)  (1)

Z1=r0*sin(A)−(p1−pc)*k*cos(A)  (2)

In the Expressions, r0 is a distance (μm) from the center O to the focalpoint F; A is an A-axis angle; p1 is a detected pixel position (pixel);and pc is the central axis position (pixel) of the detector 18. Further,k (μm/pixel) is a size of one pixel on the focal plane and is obtainedfrom the pixel size, the magnification, and the like of the detector 18.The R- and Z-positions of the edge position D or E can be calculatedfrom the Expressions (1) and (2). Note that the R- and Z-positionscorrespond to coordinates (R, Z) in the R- and Z-directions when thecenter O is defined as the origin point (0, 0).

For example, when A=+30°, the edge positions D and E correspond to 307(pixel) and 550 (pixel), respectively. The R-position (R1) and theZ-position (Z1) can be obtained by substituting these values for p1 inthe Expressions (1) and (2), respectively.

FIG. 10 is a graph showing an edge shape obtained by measuring the edgepart 31 of the substrate 30. That is, FIG. 10 shows a shape that isobtained by connecting measurement data of a plurality of edge positionsD and E with one another.

As described above, the R- and Z-positions can be obtained from the edgeposition D by using the Expressions (1) and (2). Similarly, the R- andZ-positions can be obtained from the edge position E by using theExpressions (1) and (2). Note that when there is a large differencebetween the R- and Z-positions obtained from the edge position D andthose obtained from the edge position E, a calibration may be performed.For example, a calibration value(s) may be added to the R- andZ-positions obtained from the edge position D so that they coincide withcounterpart positions. Alternatively, a calibration value(s) may beadded to the R- and Z-positions obtained from the edge position E.

Note that in FIG. 10, an end surface along the direction perpendicularto the front surface 33 and the rear surface 34 of the substrate 30 isreferred to as a side-end surface 35. An inclined surface between theside-end surface 35 and the front surface 33 is referred to as an upperbevel part 37 and an inclined surface between the side-end surface 35and the rear surface 34 is referred to as a lower bevel part 38.

As described above, an edge profile on the RZ-cross section can beobtained by measuring the edge positions D and E while changing theA-axis angle. The processing unit 50 obtains the edge profile based on adetection result obtained by the detector 18. Specifically, peakpositions of the intensity of the reflected light in the detector 18 areconverted into position coordinates on the RZ-plane. In this way, theedge profile can be accurately measured.

Since the edge profile can be measured just by changing the A-axis, theconfiguration of the apparatus can be simplified. In the confocaloptical system, it is possible to measure the edge shape withoutscanning (i.e., continuously or successively moving) the objective lens17 in the optical-axis direction. That is, it is possible to perform themeasurement without adjusting the height of the focal point. Therefore,it is possible to accurately measure the edge shape in a short time.

Further, it is possible to measure the edge shape over the entirecircumference of the substrate 30 by measuring the edge positions D andE while rotating the stage 20 shown in FIG. 1. FIG. 11 is a flowchartshowing a method for measuring an edge shape over the entirecircumference.

Firstly, the θ-rotation and the scanning of the A-axis are performed(S21). Specifically, the processing unit 50 rotates the stage 20 at aconstant speed so that the rotational speed of the stage 20 iscontinuously changed. Further, the processing unit 50 controls themoving mechanism 40 so that the A-axis angle is continuously changed oris changed in a stepwise manner. Then, a profile shape over the entirecircumference of the substrate 30 is measured (S22). The processing unit50 collects the A-axis angle and the θ-angle as well as detection datadetected by the detector 18. Therefore, by using the above-describedtechnique, an edge position for each 0-angle and for each A-axis anglecan be measured.

Note that the rotational speed of the stage 20 may be 5 rps. Further, itis assumed that a measurement time for one substrate 30 is, for example,30 seconds. In this case, the substrate 30 rotates 150 times during themeasurement. Therefore, there are 150 measurement points on eachRZ-plane.

As described above, the edge position over the entire circumference canbe measured by detecting the reflected light while rotating the stage20. Further, the edge shape over the entire circumference of thesubstrate 30 can be measured by changing the A-axis angle. Therefore, itis possible to evaluate variations among edge shapes. Further, it ispossible to measure the edge shape over the entire circumference of onesubstrate 30 in a short time of about 30 seconds. Therefore, it ispossible to accurately measure the edge shape in a short time.

Note that the above-described processes are performed in the processingunit 50. Specifically, the above-described arithmetic processing can becarried out by having a processor provided in the processing unit 50execute a computer program. Needless to mention, a part of or all of theprocessing may be carried out by using hardware such as an analoguecircuit or the like. Note that the processing unit 50 is not limited toa physically single apparatus and part of the processing may be carriedout by a physically different apparatus.

Next, a measurement result of an edge shape over the entirecircumference is described. FIG. 12 is a diagram for explaining featurevalues of each part of the edge part. As shown in FIG. 12, the thicknessof the substrate in the Z-direction is referred to as a wafer thicknessWT. The height of the side-end surface 35 of the edge part 31 in theZ-direction is referred to as an APEX length AP. The angle formedbetween the upper bevel part 37 and the front surface 33 is referred toas a TB (Top Bevel) angle TBA. The height of the upper bevel part 37 inthe Z-direction is referred to as a TB height TBL1 and the width of theupper bevel part 37 in the R-direction is referred to as a TB widthTBL2.

FIGS. 13 to 16 are graphs showing θ-dependence of feature valuesrepresenting the edge shape. FIG. 13 is a graph showing changes in thewafer thickness WT according to the θ-angle. In FIG. 13, a horizontalaxis indicates θ-angles and a vertical axis indicates wafer thicknessesWT. FIG. 14 shows changes in the TB angle TBA according to the θ-angle.In FIG. 14, a horizontal axis indicates θ-angles and a vertical axisindicates TB angles TBA.

FIG. 15 is a graph showing changes in the APEX length AP according tothe θ-angle. In FIG. 15, a horizontal axis indicates θ-angles and avertical axis indicates APEX lengths AP. FIG. 16 is a graph showing theTB height TBL1 according to the θ-angle. In FIG. 16, a horizontal axisindicates θ-angles and a vertical axis indicates TB heights TBL1. Asdescribed above, the processing unit 50 can display the θ-dependence offeature values representing the edge shape in the form of a graph.

As described above, it is possible to acquire detailed shape data on theedge shape over the entire periphery of the wafer. In the measurementmethod according to the present embodiment, it is possible to acquire asufficient number of detection data in a short time. Therefore, it ispossible to obtain data on feature values such as the wafer thicknessWT, the APEX length AP, the TB angle TBA, the TB height TBL1, and the TBwidth TBL2 over the entire circumference.

The processing unit 50 can display such feature values in the form of atwo-dimensional graph. For example, the processing unit 50 displays agraph in which a horizontal axis indicates θ-angles and a vertical axisindicates feature values in a monitor. By displaying the θ-dependence offeature values according to the edge position in the form of a graph, auser can easily recognize variations of edge shapes and a distributionthereof. Therefore, the user can appropriately evaluate and managequality of the edge part 31.

FIG. 17 shows an average profile E[r](φ) and ±3σ profiles of an edgeover the entire circumference. In FIG. 17, the average profile E[r](φ)and the ±3σ profiles at the edge position are shown on the left side.Further, in FIG. 17, parts of the profiles are shown in an enlargedmanner on the right side. Note that the average profile E[r](φ)corresponds to an edge position that is obtained by averaging data forθ=0° to 360°.

Specifically, coordinates (r, φ) of the edge position in a polarcoordinate system are obtained from coordinates (R, Z) of the edgeposition in an orthogonal coordinate system. Note that the coordinates(r, φ) represents the edge position in the polar coordinate system inwhich the center O is defined as the origin point. A radius r is a valueindicating a projecting length at the edge position and is used as afeature value representing the edge position. An angle φ is a valueindicating an angle at the center O.

The average profile E[r](φ) is obtained by averaging the whole data onthe radius r obtained in a range of 0 to 360°. For example, theprocessing unit 50 obtains an average value and a standard deviation σof the radius r for every angle φ. Then, the average value of the radiusr according to the angle φ becomes the average profile E[r](φ). Theprofiles for ±3σ correspond to E[r](φ)+3σ[r](φ) and E[r](φ)−3σ[r](φ).

Based on FIG. 17, it is understood that the standard deviation σ islarge in the bevel part of the edge part 31. That is, variations of theedge position in the φ-direction are large in the bevel part. Theprocessing unit 50 displays, as feature values, the average profileE[r](φ) and the profiles for ±3σ in a two-dimensional graph. A user caneasily recognize the variations of the edge shape and the distributionthereof. Therefore, the user can appropriately evaluate and managequality of the edge part 31.

FIG. 18 is a graph showing two-dimensionally extended unevenness dataΔr(θ, φ) of the edge position over the entire circumference. In FIG. 18,a horizontal axis indicates angles θ and s vertical axis indicatesangles φ. The unevenness data Δr(θ, φ) is data indicating deviations ofthe radius r from the average profile E[r](φ). In particular, theunevenness data Δr(θ, φ) is expressed by the following Expression (3).

Δr(θ,φ)=r(θ,φ)−E[r](φ)  (3)

In FIG. 18, the value Δr(θ, φ) is expressed by a gray scale. The morethe edge position projects outside, the lighter color (the closer towhite) it is displayed with. Further, the deeper the edge position isrecessed, the darker color (the closer to black) it is displayed with.For example, it is understood that the edge position projects in a rangeof θ=45° to 60° and φ=−80° to −30°. Note that although the value Δr(θ,φ) is expressed by a gray scale in FIG. 18, it can be expressed by acolor image.

As described above, the processing unit 50 displays, as the featurevalue according to the edge position, the unevenness data Δr(θ, φ) inthe monitor. The processing unit 50 displays the unevenness data Δr(θ,φ) in the form of a two-dimensional map. The processing unit 50 displaysa graph in which a horizontal axis indicates θ-angles and the unevennessdata Δr(θ, φ) is expressed by shading or a color image on the monitor.The vertical axis is not limited to the angle φ and may indicate valuesindicating the Z-position. As described above, by displaying theθ-dependence of feature values according to the edge position in theform of a graph, a user can easily recognize variations of edge shapesand a distribution thereof. Therefore, the user can appropriatelyevaluate and manage quality of the edge part 31.

In the measurement method according to the present embodiment, it ispossible to acquire a sufficient number of detection data in a shorttime. Therefore, it is possible to two-dimensionally extend theunevenness data Δr(θ, φ) indicating unevenness, obtained from theaverage value of the edge value, and thereby converting it into a graph.By measuring the edge position over the entire circumference asmeasurement data the edge position, it is possible to evaluate andmanage the edge position from various points of view.

The processing unit 50 displays the graphs shown in FIGS. 13 to 18 inthe monitor. In this way, a user can easily recognize variations of theedge shape.

Some or all of the above-described processes may be performed by acomputer program. The above-described program can be stored in varioustypes of non-transitory computer readable media and thereby supplied tothe computer. The non-transitory computer readable media includesvarious types of tangible storage media. Examples of the non-transitorycomputer readable media include a magnetic recording medium (such as aflexible disk, a magnetic tape, and a hard disk drive), a magneto-opticrecording medium (such as a magneto-optic disk), a CD-ROM (Read OnlyMemory), a CD-R, and a CD-R/W, and a semiconductor memory (such as amask ROM, a PROM (Programmable ROM), an EPROM (Erasable PROM), a flashROM, and a RAM (Random Access Memory)). Further, the program can besupplied to the computer by using various types of transitory computerreadable media. Examples of the transitory computer readable mediainclude an electrical signal, an optical signal, and an electromagneticwave. The transitory computer readable media can be used to supplyprograms to the computer through a wire communication path such as anelectrical wire and an optical fiber, or wireless communication path.

Although the embodiments according to the present disclosure have beenexplained above, the present disclosure also includes variousmodifications that do not substantially impair the purposes and theadvantages of the present disclosure. Further, the above-describedembodiments should not be used to limit the scope of the presentdisclosure.

From the disclosure thus described, it will be obvious that theembodiments of the disclosure may be varied in many ways. Suchvariations are not to be regarded as a departure from the spirit andscope of the disclosure, and all such modifications as would be obviousto one skilled in the art are intended for inclusion within the scope ofthe following claims.

1. A measurement apparatus comprising: an objective lens positioned sothat its focal plane cuts across an edge part of a substrate, andconfigured to concentrate illumination light so that a linearillumination area is formed on the focal plane; a detector comprising aplurality of pixels arranged along a direction of the linearillumination area, and configured to detect a reflected light from theedge part of the substrate through a confocal optical system; an opticalhead in which the objective lens and the detector are disposed; a movingmechanism configured to change a relative position of the optical headwith respect to the substrate so that an inclination of the focal planewith respect to the substrate is changed; and a processing unitconfigured to measure a shape of the edge part based on a position ofthe detector at which intensity of the reflected light reaches a peak.2. The measurement apparatus according to claim 1, further comprising arotatable stage configured to rotate the substrate, wherein thereflected light is detected while rotating the rotatable stage.
 3. Themeasurement apparatus according to claim 1, wherein: the movingmechanism rotationally moves the optical head around a rotational axis;and the rotational axis is perpendicular to a plane including a Z-axisparallel to a thickness direction of the substrate and an optical axisof the objective lens, and passes through the inside of the substrate.4. The measurement apparatus according to claim 1, wherein theprocessing unit converts the position at which the intensity of thereflected light reaches the peak in the detector into an edge positionon a plane including a Z-axis along a thickness direction of thesubstrate and an optical axis of the objective lens.
 5. The measurementapparatus according to claim 4, wherein the processing unit obtains twoedge positions disposed on both sides of the optical axis of theobjective lens.
 6. The measurement apparatus according to claim 1,wherein a graph showing angle dependence of a feature value representingan edge shape is displayed.
 7. A measurement method using a measurementapparatus, the measurement apparatus comprising: an objective lenspositioned so that its focal plane cuts across an edge part of asubstrate, and configured to concentrate illumination light so that alinear illumination area is formed on the focal plane; a detectorcomprising a plurality of pixels arranged along a direction of thelinear illumination area, and configured to detect a reflected lightfrom the edge part of the substrate through a confocal optical system;and an optical head in which the objective lens and the detector aredisposed, the measurement method comprising: changing a relativeposition of the optical head with respect to the substrate so that aninclination of the focal plane with respect to the substrate is changed;and measuring a shape of the edge part based on a position of thedetector at which intensity of the reflected light reaches a peak. 8.The measurement method according to claim 7, wherein the reflected lightis detected while rotating the substrate.
 9. The measurement methodaccording to claim 7, wherein: in the changing the relative position ofthe optical head, the optical head is rotationally moved around arotational axis; and the rotational axis is perpendicular to a planeincluding a Z-axis parallel to a thickness direction of the substrateand an optical axis of the objective lens, and passes through the insideof the substrate.
 10. The measurement method according to claim 7,wherein in the measuring the shape of the edge part, the position atwhich the intensity of the reflected light reaches the peak in thedetector is converted into an edge position on a plane including aZ-axis along a thickness direction of the substrate and an optical axisof the objective lens.
 11. The measurement method according to claim 10,wherein in the measuring the shape of the edge part, two edge positionsdisposed on both sides of an optical axis of the objective lens areobtained.
 12. The measurement method according to claim 7, wherein agraph showing angle dependence of a feature value representing an edgeshape is displayed.